[meteorite-list] Comet 2013 A1 (Siding Spring) Will Make A Very Close Approach To Mars In October 2014

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Tue, 5 Mar 2013 10:06:15 -0800 (PST)
Message-ID: <201303051806.r25I6G7f021148_at_zagami.jpl.nasa.gov>

http://neo.jpl.nasa.gov/news/news179.html

Comet 2013 A1 (Siding Spring) will make a very close approach to
Mars in October 2014

NASA/JPL Near-Earth Object Program Office
March 5, 2013

On Oct. 19, 2014, Comet 2013 A1 (Siding Spring) will pass
extraordinarily close to Mars, almost certainly within 300,000 km of the
planet and possibly much closer. Our current best estimate has it
passing about 50,000 km from the surface of Mars. This is about 2.5
times the distance of Mars' outermost satellite Deimos or less than
twice the Earth close approach distance of 2012 DA14 on February 15,
2013. Since the observation span available for orbit determination is
still relatively short, the current orbit is quite uncertain and the
nominal close approach distance will change as additional observations
are included in future orbit estimates. Currently, Mars lies directly
within the range of possible paths for the comet and we can't exclude
the possibility that the comet might impact Mars. Our current estimate
for the impact probability is less than one in six hundred and we expect
that future observations will allow us to completely rule out a Mars
impact.

Although the current heliocentric orbit is hyperbolic (i.e.,
eccentricity greater than one), the orbit is elliptic when expressed in
the frame of the solar system's barycenter. After more than a million
year journey, this comet is arriving from our solar system's distant
Oort cloud. It could be complete with the volatile gases that short
period comets often lack due to their frequent returns to the sun's
neighborhood.

During the close Mars approach, the comet will likely achieve a total
visual magnitude of zero or brighter as seen from Mars-based assets. The
attached illustration shows the comet's approximate, apparent visual
magnitude and its solar elongation angle as a function of time as seen
from Mars. Because the comet's apparent magnitude is so uncertain, the
brightness curve was cut off at apparent visual magnitude zero. However,
the comet may get brighter than magnitude zero as seen from Mars. From
Earth, the comet will not likely reach naked eye brightness but it could
brighten to visual magnitude 8 as seen from the southern hemisphere in
mid-September 2014.

[Illustration]
This illustration, prepared by Jon Giorgini, shows the apparent total
visual magnitude and solar elongation angle as seen from the center of
Mars

Rob McNaught discovered Comet 2013 A1 Siding Spring on January 3, 2013
at Siding Spring Observatory in Australia. Pre-discovery observations
located in the archives have extended the observation interval back to
Oct. 4, 2012.
Received on Tue 05 Mar 2013 01:06:15 PM PST